Abstract
Recent psycho-physiological studies have revealed close relationships between human mental stresses and secretion of hormones and/or immunological substances. However, a precise elaboration of fluctuations in the secretion of these biomarkers in the time series against stress; especially against a rather mild stressful task is not yet clearly illuminated. In this study, we used the cortisol, a major glucocorticoid, as a biomarker of mental stress for 1) illustrating the precise stress-response in the time series, and 2) investigating a congruity of cortisol as the biomarker for a mild mental workload. In the experiment, ten male university students were inscribed to conduct a simple, easy, and monotonous mental arithmetic task for about an hour with intermissions, so as to emulate a mild mental workload. As a developing result, salivary cortisol concentration depicted an accumulative increase during mild mental workloads, while no marked difference was obtained in the heart rate and its variability. It suggests the slow and long-lasting properties in the stress-response of the cortisol unlike as in autonomous nervous system indices, and therefore plausibly demonstrates the possible candidacy of cortisol as a biomarker for a mild mental load. Finally, the possible applications of cortisol for an array of biofeedback studies are discussed as that cortisol could be an alternative marker for evaluating the physiological effects driven by the series of biofeedback treatments, because of its sustentive stressresponse for a long time range and/or accumulative changing profile.
